Both in industry and in the domestic sector, solid particles often have to be separated from fluid media, such as gases or liquids. Examples of this are centrifugal drums, such as, for example, a washing machine drum for removing water from the clean laundry. Further examples are screen walls and filter means for filter discs, filter plates or filter drums for removing solid particles from liquid media, for example water or oil, or from gaseous media, for example smoke gases, air-conditioned air, contaminated industrial gases or compressed air. In this context, mostly, as high a degree of separation of the liquid or gaseous medium from the solid is to be attained. In order to achieve a high degree of separation, compression or acceleration forces are required which press the liquid or gaseous medium preferably through a permeable, for example holed or perforated or fine-mesh partition, for example in the form of a filter support or filter means. these compression or acceleration forces are necessary in order to accelerate the medium so as to overcome the frictional forces between the fluid, the solid particles and the wall and so as to guide the fluid through the partition on which solid particles can settle as a filter cake. If the degree of separation of the solids from the fluid is the same, the magnitude of these compression or acceleration forces required is determined essentially by the geometric configuration of the wall and of the arrangement of the holes in the partition.
One disadvantage, in this case, is, in particular, that high acceleration and compression forces subject the permeable wall, such as the filter support and filter means, to high mechanical load and, furthermore, require a high outlay in terms of energy in order to be generated.
Moreover, particularly in the chemical, pharmaceutical and gas industry, fluids have to be apportioned or metered. This is to take place as far as possible by simple means. Furthermore, the dwell time of the fluids in the assembly should often be as uniform as possible for reasons of reaction conditions and process engineering. Dead water zones and the local build-up of fluids should therefore as far as possible be avoided.
These complex inter-relationships are explained in more detail as an example of a washing machine drum and a partition for a filter.
The disadvantages arising as a result of high compression and acceleration forces are reflected, in the case of a washing machine drum, particularly in that the laundry is pressed into the holes of the drum wall during spinning. This gives rise to undesirable dents in the form of dimples in the spun laundry and, furthermore, to small fibre particles which pass through the holes into the tub and from there into the screen. This is undesirable particularly in the case of laundry consisting of fine textile. So as not to subject the laundry to excessive load, therefore, the washing lye is often not removed from the cleaned laundry during spinning to as great an extent as will be possible in technical terms. The residual moisture of the spun laundry, as a rule, is then subsequently removed at a later stage by means of energy-intensive drying.
DE 10 2005 026 175 A1 discloses a drum for laundry treatment machines, which is equipped with elliptic indentations which point in the direction of the interior of the drum. Since a plane wall surface or a cylindrical surface area cannot be filled completely in geometric terms with the aid of an elliptic or circular configuration of these indentations, there always remains a region of the originally non-structured plane wall or of the cylindrical surface area which is not covered by the elliptic or circular indentations. The holes for the lye outlet, called flood holes below, are arranged in this non-structured region of the drum which is furthest away from the drum axis in the radial direction. This gives rise in the region of the flood holes, with the spinning rotational speed of the drum being the same, to the highest centrifugal force for removing the lye from the washing drum. What is unsatisfactory in this case is that the flow of the lye in this non-structured region of the drum wall, in which the flood holes are also arranged, does not experience any geometric inclination perpendicularly to the drum wall. There is therefore also no geometric gradient which assists an accelerated outflow of the lye towards the flood holes. A geometrically radial flow gradient exists solely in the wall regions of the indentations, but not in the region of the outer drum wall where the flood holes are also arranged.
DE 19954027 A1 discloses a device for producing a casing of a washing machine drum which is provided with a hexagonal honeycomb structure.
With the aid of this honeycomb-shaped surface, the washing liquid which flows along the drum wall is steered gently back and forth on the vaulted honeycomb structures. An advantageous swirling of the flow thus takes place. The honeycomb structures possess approximately the contour of the vault structures (EP 0693008), the troughs directed towards the interior of the drum being in each case framed by folds and therefore filling the surface area of the drum completely. The flood holes are in this case arranged at the star points of the hexagonal holes. This affords an improvement, as compared with DE 10 2005 026 175 A1, because the flood holes from DE 19954027 A1 are not arranged on a smooth unitary cylindrical surface, but only on a narrow, for example linear surface of the folds. As a result, in the drum from DE 19954027 A1, the outflow of the lye during spinning is improved, as compared with the drum from DE 10 2005 026 175 A1. However, this geometric arrangement of the folds and of the flood holes in DE 19954027 A1 is not yet satisfactory, because, for the lye liquid to be removed during spinning, no radial gradient for the flow from the folds towards the flood holes exists in the region of the folds. Since the washing lye cannot yet be separated as efficiently as possible from the laundry in this way, the residual moisture of the laundry is removed, as a rule, by means of energy-intensive thermal drying in the laundry dryer.
In the case of a partition for filter discs, filter plates or filter drums and for centrifuging to remove solid particles from liquid media, such as water or oil, or from gaseous media, such as smoke gases, air-conditioned air, contaminated industrial gases or compressed air, for example, a screen wall has to absorb the compression forces required during filtration. The partition for a filter often consists of a filter support and of the filter means, in particular a close-mesh net, mixed fibres, synthetic fibres, glass fibres or foam materials. The filter support has the task of receiving usually soft and fine filter means and of absorbing the compression forces. These compression forces arise particularly due to the fact that the fluid to be separated from the solid particles has to be pressed through the filter means and the filter cake which is formed on the latter. These compression forces require a dimensional stability of the screen wall or of the filter support which is assisted by a small number of holes in the screen wall or filter support. The problem, then, is that, in the region of the non-holed screen wall, the fluid to be separated may build up and therefore has to be conducted along an extended flow path to the hole in the screen wall or filter support. This, in turn, requires an increased pressure for separating the solid particles from the fluid.
WO 98/40910 and US 2005/0252182 A1 describe ribbed or corrugated filter means in which, although they have a stiffening action, the stiffening is effective only in the direction of the profiling. The ribbed or corrugated filter means remains flexurally soft perpendicularly to the profiling. This has an adverse effect on the rigidity of, for example, filter discs or filter plates and also on cylindrical or conical wound modules which possess their profilings, in particular corrugations or ribs, in the axial direction of the module. WO 2005/08 24 84 A1 describes a filter element which contains a coarse-mesh cylinder as a filter support and a fan-shaped filter means. In order to save costs, it will be desirable to stiffen the filter means such that it at the same time also assumes the function of a filter support. There would therefore be no need for a filter support.
There are already in existence fine-mesh metal or plastic fabrics with screen widths into the μm range which are suitable as filter means for coarse particles of about 40 μm and for smaller particles of about a few μm, but often do not have a sufficient dimensional stability for absorbing the compression forces (without an additional filter support). Wound modules therefore often require a complicated set-up consisting of a filter means and filter support (M. Zogg: Einführung in die mechanische Verfahrenstechnik [Introduction to mechanical process engineering]; ISBN: 3-51906319-0; section 4.1.2: Querstromfiltration [Cross-flow filtration], pages 123-128).
To clean the filter units without the required demounting or exchange of the filter means, in particular, cleaning by means of pressure pulses is, of course, carried out, for example of a tubular filter (M. Stieβ: Mechanische Verfahrenstechnik 2 [Mechanical processing engineering 2]; Springer Verlag, 1997; section 7.3.2.3: Bauarten von Abreinigungsfiltern [Types of cleaning filters], page 27). In this case, a pressure pulse is generated opposite to the normal flow direction, in order to throw off the accumulated filter cake. The disadvantage of this is that an additional supporting cage is often necessary for receiving the filter means, for example a tubular filter. It will be desirable, furthermore, to have an improved hydrodynamic rinsing-free effect in which the accumulation of solid particles on the filter means is reduced even during the operation of the filter. The time interval for the use of a filter means (batch operation) until exchange or cleaning could thereby be prolonged. All this should be capable of being implemented at as low an outlay as possible in terms of apparatus.